1. Field of the Invention
This invention relates to a multifunction fiber optic bundle sensitive probe, and, more particularly, to a sensing system for the fiber optic probe that provides automatic adjustment of the changes in the intensity of the reflected light.
Fiber optic probes are flexible contactless sensors, which use light beams transmitted from light sources through bundles of optical fibers to reflected targets. Part of the light beam is reflected off the target and returned along receiving fibers in the bundle back to a light intensity sensor or sensors in the probe module. The intensity of the reflected light is a function of: the distance, Z, and two inclination angles, and .beta., between the probe tip and target; the luminous reflectance, R.sub.o, between the target and light beam wavelength; an average light intensity, I.sub.o, and the light intensity angle distribution of the light sources; and the average roughness of the target surface.
The output signals of the light sensors can provide a highly precise measurement of the distance, or more importantly, of the changes in displacement, vibrations, small inclination angles or average roughness. However, because of variations in certain operating parameters such as luminous reflectance of the target, changes in intensity of the light sources, temperature changes, and other factors that influence light conductivity, it is necessary to separate the information about the various parameters using different channels, and to make adjustments through the sensing system if any of these factors change.
This and other objects of the invention are attained in an embodiment having a multichannel fiber optic bundle (MFOB) with a sensitive probe tip with three branches of two receiving types of channels and one transmitting channel, which provides a method of sensing whereby four main signals are directed to measuring various parameters and two signals are directed to compensation and roughness measurements.
2. Prior Art Statement
Many fiber optic probes have been designed.
U.S. Pat. Nos. 4,254,331 to Dorman et al. and 4,247,764 to Kissinger describe fiber optic instruments for measuring dynamic changes in the gap between a probe tip and a target, the instrument having a light source, two sensors and one light conducting cable. The device incorporates the regulation of equal mean intensity at the reflected light sensor, despite changes in target reflectivity and cable light conductance.
U.S. Pat. No. 3,327,584 to Kissinger describes a fiber optic probe which is highly sensitive and unaffected by temperature or environment. It senses the position of a test object and uses different diameters and locations of two light receiving groups to compensate for variations.
U.S. Pat. No. 4,488,813 to Kissinger describes a device that employs dual probes to create an output signal having a gap calibration which is independent of surface reflectance.
U.S. Pat. No. 3,919,546 to Lutus describes a photo-electric apparatus for tracking a periodically moving object in order to provide an accurate electrical signal corresponding to the motion of the object. The device incorporates a feedback path that compensates for the drift in the photo-cell and light source caused by ambient temperature changes, foreign matter and aging.
U.S. Pat. No. 4,701,610 to Hoogenboom describes a fiber optic proximity sensor for narrow targets with reflectivity compensation. The device generates an output signal formula from two sensor signals and uses a scaling constant, determined from the response characteristics.
U.S. Pat. No. 4,692,611 to Hoogenboom describes a fiber optic proximity sensor with feedback servo-imaging means, with two bifurcate fiber optic bundles arranged in parallel with the reflected light from the target being transmitted to two separate sensors. The output difference of the sensors is used to derive a control signal for tracking the target, then moving the imaging means in response.
U.S. Pat. No. 4,674,882 to Dorman et al. describes a precision optical displacement measuring instrument which utilizes a servo controlled fiber optic sensor to measure the displacement of the target, such that the fiber optic sensor and lens assembly are vibrated toward and away from the target.
However, none of these inventions discloses a fiber optic bundle arranged with a plurality of receiving and transmitting channels in a 3*3 matrix formation for multichannel transmitting and receiving, and to a sensing system used therewith for automatically compensating for changes in the intensity of the light beam.